When you select a certificate and choose the Certificate menu Save command, you save the selected certificate and its private key to a PKCS#12 file. That file can be loaded into tQSLCert later using the File menu Load Certificate File command. (PKCS#12 is a standard format for containing digital certificates, so the saved file can also be loaded into other PKCS#12 compliant systems, such as Microsoft Windows.)
You will first be presented with a file selection dialog, allowing you to specify the name of the file to save to.
Once you have chosen the file, you specify the password that will be used to protect the PKCS#12 file.
It's wise to protect the file with a password. If you do not, anyone who gains posession of the file will be able to use the included certificate and private key to create digital signatures using your identity. You can choose not to use a password, but you are responsible for keeping your private information private!
Note: If the private key for the certificate you are saving is password protected, you will have to supply the password to unlock the key so it can be saved in the PKCS#12 file. If needed, you will be prompted to supply the password.
Note: The saved PKCS#12 file contains only a single certificate. If you have more than one certificate, you should save each one to a separate PKCS#12 file.